Human neutrophils express several receptors for the Fc region of IgG molecule (FCRI, RII, and RIII) and receptors for the third component of complement, CRI and CRIII (CD11b/CD18). Although numerous studies have demonstrated that the integrity of these receptors is crucial in immune adherence and functional responses of neutrophils to different types of ligands, there is limited information regarding the effects of specific FcRs and CD11/CD18 molecules on neutrophil signal transduction pathways. Recent studies indicate that neutrophil adherence and function responses are modulated by a variety of cytokines released by leukocytes, endothelial cells, and parenchymal cells. Therefore in an effort to better define the relationship between FcR, CD11/CD18 adherence glycoproteins, and neutrophil functional responses, they propose to examine the 1) biochemical mechanisms by which specific FcRs initiate signal transduction pathways in stimulating neutrophil functional responses, 2) effect of FcR interactions with each other and with CD11/CD18 molecules on neutrophil signal transduction pathways and functional responses, 3) modulation of CD11/CD18 and FcR signal transduction mechanisms in neutrophils by cytokines TNF, GM-CSF, and INF-gamma and 4) role of the ligand size and extent and type of cross-linking of surface receptors on signal transduction pathways and functional responses. Using specific monoclonal antibodies, the biochemical signals and neutrophil response induced by immune complexes (ICs), and the ligation of each member of FcR and CD11/CD18 molecules will be examined. The effect of CD11/CD18 modulation by various ligands on the function of Fc receptors will also be studied. Monoclonal antibodies against FcRs, CD11/CD18 molecules and their respective ligands will be utilized, in free form, in conjugated form with dextran molecules, in particulate form attached to latex beads, and in non-phagocytosable form, to provide various sizes of ligands and induce different types of receptor crosslinking. In addition both soluble and surface bound ICs will be utilized. To define the signal mechanisms involved in cell activation, changes in intracellular calcium and IP3 levels, and the activity of protein kinase C and phospholipase D will be measured, along with the application of established inhibitors/ modulators of biochemical signals. The neutrophil functional responses such as 0-2 generation, lysosomal enzyme release and adherence of neutrophils to protein-coated surfaces and endothelial cells will be assessed. Standard immunofluorescent techniques and flow cytometry will be applied to quantitate surface receptor expression. It is anticipated that results of this study will provide novel insight into the interactions between FcRs and CD11/CD18 adherence glycoproteins as they relate to neutrophil activation and the potential role of selected cytokines in modulating their function. These studies will provide the basis for further investigation of neutrophil signal transduction pathways and the development of new therapeutic strategies for the treatment of inflammatory diseases.